Modbus Bridge~
Add a "Modbus bridge" functionality to a device that is otherwise serial Modbus RTU only
This feature is only included in tasmota32 binary
When compiling your build add the following to user_config_override.h:
#ifndef USE_MODBUS_BRIDGE
#define USE_MODBUS_BRIDGE // Add support for software Modbus Bridge (+3k code)
#define USE_MODBUS_BRIDGE_TCP // Add support for software Modbus TCP Bridge (Must also enable USE_MODBUS_BRIDGE)
#endif
In most cases you'll need an RS485 converter like this:
Introduction~
Connect the Modbus device to an ESP and Tasmota will create a bridge to the Modbus network.
The Modbus Bridge driver features 2 kind of bridges.
USE_MODBUS_BRIDGE: The bridge can be used by commands in the console and via MQTT messages.
USE_MODBUS_BRIDGE_TCP: The bridge can be used by commands in the console and via MQTT messages but also as Modbus TCP/IP bridge
Configuration~
First assign two GPIOs to ModBR Tx and ModBR Rx in the "Configure Module" page. The Rx/Tx are relative to the ESP device. For example with ESP-12's hardware serial, set GPIO1 as ModBR Tx and GPIO3 as ModBR Rx.
Then set baud rate with ModbusBaudRate (default is 9600).
Commands~
| Command | Parameters |
|---|---|
| ModbusSend | Sending a message to the Modbus network as JSON payload.{"deviceAddress":<value>, "functionCode":<value>, "startAddress":<value>, "type":"<value>","count":<value> "endian":<value>}"deviceAddress":1..255 = device address from the Modbus slave."functioncode":1..6 or 15..16 = function code to send to the Modbus slave (see table below)."startaddress":1..65535 address of the first register to read."type":"<value>" Gives the type of the returned data (see table below). "count":1..n the number of values to be requested. "endian":msb,lsb Sets endian msb (big) or lsb (little) (optional). |
| ModbusBaudrate | 1200...115200 = set baudrate for serial (only 8N1 mode) in 1200 increments (default = 9600) |
| ModbusSerialConfig | Set serial protocol using data/parity/stop conventional notation (example: 8N1 or 702)0..23 = set serial protocol (3 equals 8N1) |
FunctionCode~
| Function Code | Description |
|---|---|
| 1 | Read Coils |
| 2 | Read Discrete Inputs |
| 3 | Read Multiple Holding Registers |
| 4 | Read Input Registers |
| 5 | Write Single Coil |
| 6 | Write Single Register |
| 15 | Write Multiple Coils |
| 16 | Write Multiple Registers |
Type~
| Type | Description |
|---|---|
| raw | Return or send the slave data as a raw values |
| bit | Return or send the slave data as a bit values |
| hex | Return or send the slave data as a hex values |
| float | Return or send the slave data as floats |
| uint8 | Return or send the slave data as an 8 bits unsigned int |
| uint32 | Return or send the slave data as a 32 bits unsigned int |
| uint16 | Return or send the slave data as a 16 bits unsigned int |
| uint32 | Return or send the slave data as a 32 bits unsigned int |
| int8 | Return or send the slave data as an 8 bits signed int |
| int16 | Return or send the slave data as a 16 bits signed int |
| int32 | Return or send the slave data as a 32 bits signed int |
Additional commands for USE_MODBUS_BRIDGE_TCP~
| Command | Parameters |
|---|---|
| ModbusTCPStart | <port> = start the Modbus TCP bridge on the specified port |
| ModbusTCPConnect | <port>,<ip_address> = connect to a remote Modbus TCP server on remote tcp portĖ and ip_address |
| ModbusTCPMqtt | <x> = send results queried by tcp modbus client also to mqtt when parameter is 1 |
Returned Data~
{"ModbusReceived":{"DeviceAddress":<value>,"FunctionCode":<value>,"StartAddress":<value>,"Length":<value>,"Count":<value>,"Values":[value1,value2,value3,valueN]}}
In raw mode, only the data is returned, no other fields.
Error Codes~
There are 2 types of errors, errors from the tasmotamodbus driver and errors from this Modbusbridge module.
Module Errors~
Errors from this Modbus bridge module can be recognized by MBS: MBR Send error or MBS: MBR Recv error at the start of the errormessage.
| Errorcode | Description |
|---|---|
| 1 | nodataexpected |
| 2 | wrongdeviceaddress |
| 3 | wrongfunctioncode |
| 4 | wrongstartaddress |
| 5 | wrongtype |
| 6 | wrongregistercount |
| 7 | wrongcount |
| 8 | tomanydata |
Driver Errors~
Errors from the tasmotamodbus driver can be recognized by MBS: MBR Driver error
| Errorcode | Description |
|---|---|
| 1 | Illegal Function |
| 2 | Illegal Data Address |
| 3 | Illegal Data Value |
| 4 | Slave Error |
| 5 | Acknowledge but not finished (no error) |
| 6 | Slave Busy |
| 7 | Not enough minimal data received |
| 8 | Memory Parity error |
| 9 | Crc error |
| 10 | Gateway Path Unavailable |
| 11 | Gateway Target device failed to respond |
| 12 | Wrong register count |
| 13 | Register data not specified |
Example of use~
Requesting 4 holding registers starting from register 1 from slave address
Register 1~
On command:
ModBusSend {"deviceaddress": 1, "functioncode": 3, "startaddress": 1, "type":"uint16", "count":4}
Response:
RSL: RESULT = {"ModbusSend":"Done"}
RSL: RESULT = {"ModbusReceived":{"DeviceAddress":1,"FunctionCode":3,"StartAddress":1,"Length":13,"Count":4,"Values":[65282,65028,65280,65024]}}
Set coil register 1 of slaveaddress 1 to ON:~
On command:
ModBusSend {"deviceaddress": 1, "functioncode": 5, "startaddress": 1, "type":"bit", "count":1, "values":[1]}
RSL: RESULT = {"ModbusSend":"Done"}
RSL: RESULT = {"ModbusReceived":{"DeviceAddress":1,"FunctionCode":5,"StartAddress":1,"Length":8,"Count":1,"Values":[255]}}
Setting multiple coils starting from coil register 1 from slave address 1~
On command:
ModBusSend {"deviceaddress": 1, "functioncode": 15, "startaddress": 1, "type":"bit", "count":8, "values":[1,0,0,1,1,1,0,0]}
RSL: RESULT = {"ModbusSend":"Done"}
RSL: RESULT = {"ModbusReceived":{"DeviceAddress":1,"FunctionCode":15,"StartAddress":1,"Length":8,"Count":1}}
Additional resources~
Tasmota Pull Request
Modbus Protocol
More Modbus information